An electronic device having a touchscreen user interface, such as a tablet, smartphone, or tabletop display, can be configured to receive single-touch input, multi-touch input, or both, via its touchscreen display. Input generally includes touches, which are often localized to one particular point of contact with the touchscreen, while gestures involve movement of a contact point (e.g., dragging one's finger) along the touchscreen. Input received via the touchscreen display can be interpreted as commands to alter the content displayed in a view on the touchscreen, for example to scroll, zoom in/out (magnify or reduce), or rotate the content within the view.
Some touch input is more easily conceptualized by users using multi-touch gesture input than by single-touch input. For example, a multi-touch zoom command is commonly implemented through detection of a “pinch” gesture, in which the user simultaneously touches the touchscreen at two initial contact points, usually using the thumb and index finger, then moves the contact points apart or together while maintaining contact on the touchscreen. The simultaneous touch events are detected and interpreted by the device processor as a command to magnify or reduce the displayed size of the content in the current view shown on the display, optionally with a magnification factor calculated from the distance covered by the pinch gesture. The user can easily correlate the pinch gesture to the two-dimensional transformation of zooming, since the user's action mimics the visual effect. The user is also able to control the amount of zooming based on the gesture dimensions.
However, gesture input is constrained not only by the physical size of the touchscreen available to receive the input, but also by the user's own dexterity and flexibility. Typically, only one hand is available to carry out a gesture since the other hand is often employed in holding the electronic device; as a result, such input is conventionally restricted to gestures that can be carried out using one hand. Furthermore, multi-touch input may be less accessible to users with finger or wrist joint problems.